1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a preamplifier circuit configurable to allow simultaneous read and write operations for self-servo writing a disk drive.
2. Description of the Prior Art
Disk drives for computer systems comprise a disk for storing data and a head actuated radially over the disk for writing data to and reading data from the disk. To effectuate the radial positioning of the head over the disk, the head is connected to the distal end of an arm which is rotated about a pivot by a rotary actuator (e.g., a voice coil motor (VCM)). The disk is typically divided into a number of concentric, radially spaced tracks, where each track is divided into a number of data sectors. The disk is typically accessed a data sector at a time by positioning the head over the track which comprises the target data sector. As the disk spins, the head writes transitions (e.g., magnetic transitions) in the data sector to record data, and during read operations senses the transitions to recover the recorded data.
Accurate reproduction of the recorded data requires the head to be positioned very close to the centerline of the target data sector during both write and read operations. Thus, accessing a target data sector involves positioning or xe2x80x9cseekingxe2x80x9d the head to the target track, and then maintaining centerline xe2x80x9ctrackingxe2x80x9d while data is written to or read from the disk. A closed loop servo system typically performs the seeking and tracking operations by controlling the rotary actuator in response to position information generated from the head.
A well known technique for generating the head position control information is to record servo information in servo sectors disbursed circumferentially about the disk, xe2x80x9cembeddedxe2x80x9d with the data sectors. This is illustrated in FIG. 1 which shows a disk 2 comprising a number of concentric tracks 4 and a number of embedded servo sectors 6. Each servo sector 6 comprises a preamble 8, a sync mark 10, servo data 12, and servo bursts 14. The preamble 8 comprises a periodic pattern which allows proper gain adjustment and timing synchronization of the read signal, and the sync mark 10 comprises a special pattern for symbol synchronizing to the servo data 12. The servo data 12 comprises identification information, such as sector identification data and a track address. The servo control system reads the track address during seeks to derive a coarse position for the head with respect to the target track. The track addresses are recorded using a phase coherent Gray code so that the track addresses can be accurately detected when the head is flying between tracks. The servo bursts 14 in the servo sectors 6 comprise groups of consecutive transitions (e.g., A, B, C and D bursts) which are recorded at precise intervals and offsets with respect to the track centerline. Fine head position control information is derived from the servo bursts 14 for use in centerline tracking while writing data to and reading data from the target track.
The embedded servo sectors 6 are written to the disk 2 as part of the manufacturing process. Conventionally, an external servo writer has been employed which writes the embedded servo sectors 6 to the disks by processing each head disk assembly (HDA) in an assembly line fashion. The external servo writers employ very precise head positioning mechanics, such as a laser interferometer, for positioning the head at precise radial locations with respect to previously servo-written tracks so as to achieve very high track densities.
There are certain drawbacks associated with using external servo writers to write the embedded servo sectors 6 during manufacturing. Namely, the HDA is typically exposed to the environment through apertures which allow access to the disk drive""s actuator arm and the insertion of a clock head which requires the servo writing procedure to take place in a clean room. Further, the manufacturing throughput is limited by the number of servo writers available, and the cost of each servo writer and clean room becomes very expensive to duplicate.
Attempts to overcome these drawbacks include a xe2x80x9cself-servo writingxe2x80x9d technique wherein components internal to the disk drive are employed to perform the servo writing function. Self-servo writing does not require a clean room since the embedded servo sectors are written by the disk drive after the HDA has been sealed. Further, self-servo writing can be carried out autonomously within each disk drive, thereby obviating the expensive external servo writer stations.
U.S. Pat. No. 5,949,603 as well as IBM Technical Disclosure Bulletin, Vol. 33, No. 5 (October 1990) disclose in an article entitled xe2x80x9cRegenerative Clock Technique for Servo Track Writesxe2x80x9d a technique for self-servo writing wherein the servo sectors are written relative to clock data disbursed around the disk and propagated from track to track. The clock data is first written to a xe2x80x9cseedxe2x80x9d track (e.g., at the inner diameter of the disk) from which the clock data as well as the servo sectors are propagated to the remaining tracks. The head is positioned over the seed track and, while reading the clock data in the seed track, the head is moved away from the seed track until the amplitude of the read signal decreases to some predetermined level. Then the clock data and servo sectors are written to the first track adjacent to the seed track. This process is repeated for the next and subsequent tracks until the embedded servo sectors have been written over the entire surface of the disk. Because the head cannot read and write simultaneously, the clock data is propagated in even and odd interleaves. When servo writing a current track, the even clock data from a previously servo-written track is read to derive timing and head position control information while writing the odd clock data and servo sectors to the current track. When servo writing the next track, the odd clock data from the previously servo-written track is read to derive timing and head position control information while writing the even clock data and servo sectors to the next track, and so on.
This process is illustrated in FIG. 2A and FIG. 2B. FIG. 2A shows a read element being offset from a current track until the amplitude of the read signal decreases to a predetermined level while reading the A (even) clock data. Thereafter a write element begins writing the B (odd) clock data and servo sectors (SS) for the next track. Notice that the head never simultaneously reads and writes because writing to the next track occurs between the A clock data. When finished writing the B clock data and servo sectors to the track, the head is offset from the finished track until the read signal decreases to the predetermined level while reading the just-written B clock data as illustrated in FIG. 2B. The write element then writes the A clock data and the servo sectors to the next track.
When self-servo writing the disk it is important to maintain proper spacing between adjacent tracks as well as proper alignment of the servo sectors from track to track so as to achieve a high recording density (tracks per inch) as well as preserve the phase-coherent nature of the Gray code in the track addresses and proper alignment of the servo bursts. Thus, it is important for the head to maintain the desired radial offset from the previously servo-written track while writing the servo sectors to a current track. In this respect, the above-described prior art self-servo writing technique suffers because the clock data is used both for radial positioning of the head as well as circumferential timing. Various system dynamics induce noise in the read signal while reading the clock data (e.g., errors in writing the clock data, media defects, electronic noise, etc.) which translates into errors when generating the head position control information for use in maintaining the desired radial offset from the previously servo-written track while writing the servo sectors to a current track.
Prior art preamplifier circuits used in magnetic disk recording are configured by a disk control system to select a particular head for a read or write operation, but not both simultaneously. Conventional inductive heads cannot simultaneously read and write since a single inductive element (coil) is used to both read and write. The newer magnetoresistive (MR) heads comprise a separate MR read element and an inductive write element; however, writing data (transitions) to the magnetic disk using the inductive write element interferes with the operation of the MR read element. Therefore, prior art preamplifier circuits have been designed to prevent simultaneous reading while writing. Prior art techniques for self-servo writing a disk drive by propagating a clock pattern, such as disclosed in the aforementioned U.S. Pat. No. 5,949,603, erase the entire surface of the disk before performing the self-servo writing operation. However, this increases the time and expense of self-servo writing the disk drive.
There is, therefore, a need for a more efficient self-servo writing technique which does not require the entire surface of the disk to be erased before performing the self-servo writing operation.
The present invention may be regarded as a preamplifier circuit comprising a data input for receiving write data, a read signal output for outputting an amplified read signal, a read signal input for receiving a read signal from a read element, and a write signal output for supplying a write signal to a write element. The preamplifier circuit further comprises a first amplifier circuit, responsive to the write data, for generating the write signal supplied to the write element via the write signal output, and a second amplifier circuit for amplifying the read signal from the read element to generate the amplified read signal output via the read signal output. A head control circuit, responsive to head select data, simultaneously enables the first and second amplifier circuits to perform a simultaneous read and write operation.
The present invention may also be regarded as a disk drive comprising a disk having a plurality of tracks, a head comprising a read element and a write element, a control system, and a preamplifier circuit. The preamplifier circuit comprises a data input for receiving write data from the control system, a read signal output for outputting an amplified read signal to the control system, a read signal input for receiving a read signal from the read element, and a write signal output for supplying a write signal to the write element. A first amplifier circuit, responsive to the write data, generates the write signal supplied to the write element via the write signal output, and a second amplifier circuit amplifies the read signal from the read element to generate the amplified read signal output to the control system via the read signal output. A head control circuit, responsive to head select data received from the control system, simultaneously enables the first and second amplifier circuits to perform a simultaneous read and write operation.